Photoelectric heat control for coffee brewers



April 4, 1950 J. R. HILDRETH PHOTOELECTRIC HEAT CONTROL FOR COFFEE BREWERS Filed Sept. 6, 1947 fiwezziaz Jae? 2 jf zzdzwz 3/5 wy st Patented Apr. 4, 1.950

UNITED STATES PATENT OFFICE PHOTOELECTRIC HEAT CONTROL FOR COFFEE BREWERS 4 Claims.

This invention relates to coffee brewers of the type comprising upper and lower bowls, the upper bowl having an integral tube fitting snugly in the neck of the lower bowl the bottom of which is adapted to set upon a stove, and more particularly to the control of the heat supplied by the stove to the lower bowl during the successive phases of the coffee brewing cycle. Heretofore it has been necessary to control the heat manual- 1y, thus requiring close attention by the operator. After water from the lower bowl has remained in the upper bowl long enough to brew the coffee, the heat must be turned off to permit the coffee to descend to the lower bowl. Then it is desirable to turn on a low heat to keep the coffeeWarm.

To obtain successive bowls of coffee or uniform quality and strength, the aforesaid adjustments mustbe made at the same times in successive brewing cycles. The constant attention required to adjust the brewer at the proper timing is inconvenient for a busy housewife and, in a restaurant where a continuous supply of coffee is needed, results in additional cost for labor.

The objects of the present invention are to avoid the aforesaid inconvenience, to regulate the heat automatically, to brew each successive bowl of coffee the same length of time at the same temperature, and generally to improve the art of cofiee brewing.

In one aspect the present invention contemplates the use with a brewer of the above-mentioned type of a photoelectric element responsive to rays which are refracted when passing obliquely through the air-water surface of the liquid in the lower bowl, and a ray element for energizing the photoelectric element with rays of the aforesaid type. These elements are so positioned relatively to the lower bowl, when it is setting upon the stove, that energy from the ray element is directed L obliquely through the surface and, when the liquid in the lower bowl attains a predetermined level, impinges on the photoelectric element. Means are provided for reducing the heat supplied by the stove to the lower bowl responsive t the energization of the photoelectric element when the liquid in the lower bowl attains this predetermined level.

In another aspect the invention contemplates the use with such a brewer of a photoelectric device responsive to rays which are transmitted through water, and a ray device for energizing the photoelectric device with rays of the aforesaid type. These devices are So positioned relatively to the lower bowl, when it is setting upon 55 the stove, that energy from the ray device is directed through the liquid in the lower bowl to impinge upon the photoelectric device. Means are provided for controlling the heat supplied by the stove to the lower bowl responsive to variation of energization of the photoelectric device when the liquid in the lower bowl varies in transmittancy.

In the preferred embodiment the invention contemplates the use of a photoelectric element responsive to rays which are refracted when passing obliquely through the air-water surface. The ray element is so positioned that when the lower bowl rests on the stove the rays pass obliquely through the surface of the water in the lower bowl, and when the surface descends to a predetermined low level, the rays are refracted at this surface to the photoelectric element.

Another photoelectric device responsive to rays which are transmitted through water and another ray device are so positioned relatively to the lower bowl, when it is setting upon the stove, that energy from the ray device is directed through the liquid in the lower bowl to impinge upon the photoelectric device. Relays operated by a control circuit incorporating vacuum tubes are used to connect the resistance elements of the stove in parallel across the power supply circuit in response to the energization of the photoelectric element when the liquid in the lower bowl falls to a predetermined level. These relays reconnect resistances in series in response to a decrease in energization of the photoelectric device when the liquid in the lower bowl decreases in transmittancy. i

For purposes of illustration, a typical embodiment of the invention is shown in the accompanying drawing, in which Fig. 1 is an elevation in partial section;

Fig. 2 is a section on line 22 of Fig. l; and

Fig. 3 is a wiring diagram of the control circuit.

In the particular embodiment of the invention chosen for the purpose of illustration, a brewer, consisting of an upper bowl I with a dependent tube 2 extending into the transparent lower bowl 3, is shown in position upon an electric stove 4. The lower bowl 3 is adjacent to resistance elements such as heating coils RI and R2 which are wound in the spiral grooves 6 of the ceramic brick I. The brick 1 is supported by an arched bracket 8 fastened to the stove base 9 from which also extend the hollow arms II and I2.

-Housed in arm I2 is a ray device comprising a lamp Ll, lens 14 and an aperture plate I6.

An associated photoelectric device, such as a phototube PI of the type 868, is held by bracket I3 in a corresponding position in arm II. An aperture tube I! is mounted in the side wall of arm II adjacent to the photo-tube PI. The lamp LI and the phototube PI are relatively so Dositioned that the light beam BI from the lamp LI will pass through the lower bowl 3 and the aperture tube I to impinge upon the cathode kl (Fig. 3) of the phototube Pi. The lower end of arm I2 is used to enclose the normally closed relay I8 and the relay control circuit responsive to phototube PI which comprises a resistor TI and a vacuum tube V3 of the type 2051.

A lens barrel 26 is inserted in a hole centrally located in the ceramic brick I. The barrel 26 holds a lens 22 and an aperture plate 23 which comprise the optical system of a ray element. The associated lamp L2 of the ray element is mounted on base 9 adjacent to the lower end of the .barrel 26. A photoelectric element such as phototube P2, also of the type 868, is mounted by means of bracket 20 within the top of arm I2. An aperture tube 2I is inserted in the inclined wall of arm I2. The locations of the phototube P2 relatively to the lamp L2 will hereafter be described in connection with the operation of the invention. The lower end of arm II houses the double throw relay 2'! and the relay control circuit of the phototube P2 comprising the resistor 1'2 and the vacuum tube V4 of the type 2051.

The wiring diagram of the control circuits is shown in Fig. 3. Line terminals a and c indicatea source of alternating current supplying the phototubes PI, P2, lamps LI, L2 and the vacuum tubes V3, V4. The anode a2 is connected to terminal a which is electrically linked to anodes .al, a3, a l through the resistor TI and the relays I8, 27 respectively. Resistor r2 completes the circuit from cathode 702 to terminal 0. The cathodes lcI, k3, 704 are joined directly to terminal 0. By joining the other side of cathode k3 through lamp LI to terminal a, the cathode heating circuit is established. Lamp LI serves the dual function of reducing the supply voltage to a value suitable for cathode I63 and providing the light source for the beam BI to operate the phototube PI. Lamp L2 is similarly connected in series with the cathode k4 and performs analogous functions with respect to the phototube P2.

The grid 93 of vacuum tube V3 is connected between the resistor Ti and the anode rJI of phototube PI. The voltage drop through resistor rI decreases, making grid 93 more positive (in the conventional sense) ,as the impedance of the phototube PI increases with a diminution of the light falling upon the cathode plate kl. Grid g4 of the vacuum tube V4 is connected between cathode I02 and the resistor 12. This grid 94 becomes more positive when the .light falling on phototube P2 decreases the impedance of the tube and the voltage drop across the resistor r2 increases.

One end of each of heating coils RI, R2 is joined by wire :c which further branches through the contacts of relay 21 to terminal a. Wire 11 directly links the opposite end of heating coil R2 to terminal 0. The opposite end of heating coil RI is joined by wire a to the double pole relay I8. In the deenergized position shown, relay I8 connects (coil RI to terminal through wires 2 and 21. When relay I 8 is energized the circuit is completed from the heating coil .Rl to terminal a by means-of wires 2 and u.

from the beam Bi.

respect to the cathode R3.

To operate the brewer finely ground coffee is measured into the upper bowl I, the tube 2 of which is tightly inserted into the neck of bowl 3 containing the water w. The brewer is placed on the stove 4, the terminals a and c of which are connected to the power supply. When detent 30 is released, relay 21 parallels the heating coils RI and R2 across the power supply by connecting Wire x to terminal a. The circuit to terminal c through coil R2 is completed by wire y. The relay I8 being deenergized completes the circuit through RI by means of wires 2 and v as heretofore described.

The heat radiated from coils RI and R2 causes the water w in the lower bowl 3 to boil. As the steam pressure increases, the water 10 is forced through the tube 2 into the upper bowl I and the air-water surface descends from the level indicated at 3 until it reaches the level indicated at 52.

Lamp L2 so directs beam B2 through the water in in the lower bowl 3 that the beam is refracted to the right as it emerges from the air-water surface. When the water 20 is at a level 8, the distance from the phototube P2 to the surface is short compared to the distance from the surface to the lamp L2. The beam B2 is then refracted to impinge upon the arm [I2 well above the aperture tube 2-I. Although the angle of refraction remains constant, the increase in the distance from the phototube P2 to the surface and the decrease in the distance from the surface to the lamp L2, as the surface descends, shift the beam further towards the right, As the level s2 is reached, the beam B2 passes through the aperture tube 2I to impinge on the cathode k2. The illumination of the photocell .P2 by the beam B2 increases the conductance of the tube. The resultin increase of the voltage drop across resistor 72 makes the grid 94 of vacuum tube V4 more positive with respect to the cathode k4. As the grid 94 becomes positive, the resulting current flow through the vacuum tube V4 energizes relay 21.. The contacts of relay 2'! are moved to the position to open the circuit of the heating coils RI, B2. The relay 2.! is then held in the open position by thedetent3fi.

After the heat from the stove 4 has been interrupted by the opening of the contacts of relay 2?, the liquid which has been steeping in the upper bowl I slowly descends and mixes with the remaining water to in the lower bowl ;3. As the liquid in the lower bowl .8 rises, its reduced transmittancy, resulting from the mixing with the steeped liquid from the upper bowl I decreases the illumination reaching phototube -PI As the illumination decreases the resistance of the phototube PI increases. The g-ridg3 becomes more positive with The resulting current through tube V3 energizes the relay I8 which connects the heating coil elements RI, R2

in series between terminals :1 and c by means of wires u, w, 1/. The heat supplied :by heating coils RI, R2 in series is one fourth theheat supplied when elements RI, R2 are in parallel across terminals a and c. The coffee therefore remains hot, but does not boil and ascend to the upper bowl.

It should be understood that the present .dis' closure is for the purpose of illustration only and that this invention includes all modifica' .tions and equivalents which fall withinithescope of the appended claims.

I claim:

1. For use with a brewer of the type comprising an upper bowl having a depending tube extending into a translucent lower bowl, a stove for heating liquid in the lower bowl, a photoelectric element responsive to rays which are refracted when passing obliquely thrOugh an air-water surface, a ray element for energizing the photoelectric element with rays of the aforesaid type, said elements being so positioned relatively to the lower bowl when setting upon the stove that energy from the ray element is directed obliquely through the surface of the liquid in said lower bowl to impinge on the photoelectric element when the liquid attains a predetermined level, and means for reducing the heat supplied to the lower bowl by the stove responsive to the energlzation of said photoelectric element when the liquid in the lower bowl attains a predetermined level.

2. For use with a brewer of the type comprising an upper bowl having a depending tube extending into a translucent lower bowl, a stove for heating liquid in the lower bowl, a photoelectric element responsive to rays which are refracted when passing obliquely through an air-water surface, a ray element for energizin the photoelectric element with rays of the aforesaid type, one of said elements being positioned beneath the lower bowl when setting upon the stove, the other element relatively being so positioned above the surface of the liquid in the lower bowl that energy from the ray element is directed obliquely through the surface of said liquid in the lower bowl to impinge on the photoelectric element when the liquid attains a predetermined level, and means for reducing the heat supplied to the lower bowl by the stove responsive to the energization of said photoelectric element when the liquid in the lower bowl attains a predetermined level.

3. For use with a brewer of the type comprising an upper bowl having a depending tube extending into a translucent lower bowl, a stove for heating liquid in the lower bowl, a photoelectric element responsive to rays which are refracted when passing obliquely through an air-water surface, a ray element for energizing the photoelectrio element with rays of the aforesaid type, one

of said elements being positioned beneath the lower bowl when settin upon the stove, the other element being so positioned above the surface of the liquid in the lower bowl that energy from the ray element is directed obliquely through the surface of the liquid in said lower bowl to impinge on the photoelectric element when the liquid attains a predetermined level, a photoelectric device responsive to rays which are transmitted through water, a ray device for energizing the photoelectric device with rays of the aforesaid type, said devices being so positioned relatively to the lower bowl when setting upon the stove that energy from the ray device is directed through the liquid in the lower bowl to impinge on the photoelectric device, and means for reducing the heat supplied to the lower bowl by the stove responsive to the energization of said photoelectric element when the liquid in the lower bowl attains a predetermined level and controlling the heat supplied responsive to the variation of energization of said photoelectric device when the liquid in the lower bowl varies in transmittancy.

4. For use with a brewer of the type comprising an upper bowl having a depending tube extending into a translucent lower bowl, an electric stove with resistance elements for heating fluid in the lower bowl, a photoelectric element responsive to rays which are refracted when passing obliquely through an air-water surface, a ray element for energizing the photoelectric element with rays of the aforesaid type, one of said elements being positioned beneath the lower bowl when setting upon the stove, the other element relatively being so positioned above the surface of the liquid in the lower bowl that energy from the ray element is directed obliquely through the surface of the liquid in said lower bowl to impinge on the photoelectric element when the liquid attains a predetermined level, a photoelectric device responsive to rays which are transmitted through water, a ray device for energizing the photoelectric device with rays of the aforesaid type, said devices being so positioned relatively to the lower bowl when setting upon the stove that energy from the ray device is directed through the liquid in the lower bowl to impinge on the photoelectric device, and relays operated by control circuits incorporatin vacuum tubes for connecting said resistanc elements in parallel responsive to the energization of the photoelectric element when the liquid in the lower bowl attains a predetermined level and reconnecting said resistance elements in series in response to a decrease in energization of the photoelectric device when the liquid in the lower bowl decreases in transmittancy.

JACK R. I-IILDRETH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,939,088 Styer Dec. 12, 1933 2,070,617 Offutt Feb. 16, 1937 2,287,583 Weeks June 23, 1942 2,323,128 Hare June 29, 1943 2,436,575 Johnson Feb. 24, 1948 

